Well, all these suggestions are nice and this also looks like a nice finger exercise but you really want to start something like this only with software that's still useable somehow in 50+ yrs. So just ignore this proprietary stuff and use plain text files + grep (or something similar).
You can still use a nice frontend to the data. Vimwiki, tiddlywiki, zim wiki, etc. all store their data in plain text but let's you create these connections trivially that Zettelkasten is all about.